1. Field of the Invention
The present invention relates to a silver-based catalytic composition suitable for use in processes for the oxidation of organic compounds, particularly for the oxidation of ethylene to ethylene oxide and of methanol to formaldehyde. Also, according to another aspect, the present invention relates to a process for the oxidation of ethylene to ethylene oxide and the process for the oxidation of methanol to formaldehyde.
2. Description of the Prior Art Pat. No.
Silver has been known for some time as a catalyst in the oxidation of ethylene to ethylene oxide and in the oxidation of methanol to formaldehyde. Variable amounts of other minor ingredients are usually used with the silver with the scope of increasing the catalytic efficiency. Examples of such additional materials include: copper, barium, the alkaline earth metals, iron, manganese, cadmium, zirconium, aluminum, amongst others, both singly and in combination. There are also known silver-based catalytic compositions which include small quantities of an alkaline earth metal and a metal chosen from the third group of the Periodic Table of Elements. In fact, U.S. Pat. No. 3,461,140 describes catalytic compositions useful in the manufacture of ethylene oxide consisting of silver, an alkaline earth metal (particularly barium and calcium) and aluminum and/or boron. This patent, however, does not consider the possibility of using as a metal of the third group a metal belonging to Group IIIa of the periodic system of elements, in particular, indium. In fact, in U.S. Pat. No. 3,461,140 only aluminum is exemplified.
Prior catalytic compositions of the type described above exhibit several disadvantages. For example, apart from containing toxic materials, they have a surface area to mass ratio which decreases with time at the temperatures normally used in the above-described oxidation processes with a corresponding decrease of catalytic activity. In order to keep the productivity of the plant constant to overcome the decreased catalytic activity, one must increase the operating temperature. This has obvious disadvantages such as increased production costs and decrease in life of the catalyst.